1. Field of the Invention
The present invention relates to communication equipment and, more specifically, to equipment for wireless local area networks (WLANs).
2. Description of the Related Art
IEEE Standard 802.11 has emerged as a prevailing technology for broadband access in WLAN systems and is regarded by many as a wireless version of Ethernet. The 802.11 legacy medium access control (MAC) is based upon best-effort service, which does not support quality of service (QoS) for users or applications. However, the increasing demand for streaming voice and video transmissions, which typically have certain QoS requirements, prompted the 802.11 Working Group to begin work on an extension to the standard. The upcoming 802.11e supplement standard will define enhancements to the legacy 802.11 MAC providing a QoS support facility.
Draft standard 802.11e (version D4.0 of November, 2002), the teachings of which are incorporated herein by reference, provides two mechanisms for the support of applications with QoS requirements. The first mechanism, designated as Enhanced Distributed Coordination Function (EDCF), is based on differentiating priorities at which data traffic is to be delivered. The second mechanism allows for scheduling of transmission opportunities with the hybrid coordinator located at the access point (AP) of the WLAN.
The EDCF is based on eight priority values, designated 0 to 7, which are analogous to IEEE 802.1 d priority tags. Each data frame to be transmitted is provided with a priority value, based on which the frame is sorted into one of the following four access categories (ACs): best effort, video probe, video, and voice. Each AC contends for access to the wireless medium based on the corresponding QoS parameter set (PS) including, for example, the values of (i) CWmin and CWmax specifying the contention window and (ii) arbitration inter-frame spacing (AIFS). After winning a contention, an AC is allowed to transmit one or more frames in addition to the first frame without having to re-contend for access to the wireless medium for the transmission of the additional frames. Such transmission of multiple frames is referred to as frame bursting. Although frame bursting typically improves effective capacity of the communication channel, methods directed to efficient utilization of frame bursting by wireless stations are not sufficiently developed.